A sensitive method for light microscopic localization of brain receptors by in vitro autoradiography was developed previously in this laboratory. By this method we have mapped the locations of opiate receptors in the brains of rats and other vertebrates, including primates. Comparisons of tritiated opiate alkaloid binding with tritiated enkephaliln binding have confirmed the existence of opiate receptor subtypes. These have been related to the developing and adult dopamine system in the striatum. The possibility of pharmacological and hormonal manipulation of receptor distributions in the striatum and hypothalamus is being examined. Applications are being pursued for the concurrent study of the distributions of receptors, neuronal pathways and biologically active peptides and enzymes. The autoradiographic technique of metabolic mapping by 2-deoxyglucose has been used in functional studies of the extra-pyramidal motor system and the neuropharmacologic manipulation of this system.